We investigated the role of neuronal (type I) nitric oxide synthase (nNOS) in NMDA-mediated excitotoxicity in wild-type (SV129 and C57BL/6J) and type I NOS knock-out (nNOS Ϫ/Ϫ ) mice and examined its relationship to apoptosis. Excitotoxic lesions were produced by intrastriatal stereotactic NMDA microinjections (10-20 nmol). Lesion size was dose-and timedependent, completely blocked by MK-801 pretreatment, and smaller in nNOS knock-out mice compared with wild-type littermates (nNOS ϩ/ϩ , 11.7 Ϯ 1.7 mm 3 ; n ϭ 8; nNOS Ϫ/Ϫ , 6.4 Ϯ 1.8 mm 3 ; n ϭ 7). The density and distribution of striatal NMDA binding sites, determined by NMDA receptor autoradiography, did not differ between strains. Pharmacological inhibition of nNOS by 7-nitroindazole (50 mg/kg, i.p.) decreased NMDA lesion size by 32% in wild-type mice (n ϭ 7). Neurochemical and immunohistochemical measurements of brain nitrotyrosine, a product of peroxynitrite formation, were increased markedly in wild-type but not in the nNOS Ϫ/Ϫ mice. Moreover, elevations in 2,3-and 2,5-dihydroxybenzoic acid levels were significantly reduced in the mutant striatum, as a measure of hydroxyl radical production.The importance of apoptosis to NMDA receptor-mediated toxicity was evaluated by DNA laddering and by quantitative histochemistry [terminal deoxynucleotidyl transferasemediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) staining]. DNA laddering was first detected within lesioned tissue after 12-24 hr. TUNEL-positive cells were first observed at 12 hr, increased in number at 48 hr and 7 d, and were located predominantly in proximity to the lesion border. The density was significantly lower in nNOS Ϫ/Ϫ mice. Hence, oligonucleosomal DNA breakdown suggesting apoptosis develops as a late consequence of NMDA microinjection and is reduced in nNOS mutants. The mechanism of protection in nNOS Ϫ/Ϫ mice may relate to decreased oxygen free radical production and related NO reaction products and, in part, involves mechanisms of neuronal death associated with the delayed appearance of apoptosis.

Autoimmune hepatitis (AIH) after liver transplantation (LT) may recur and is difficult to diagnose. Our aims were to define the histopathology of and factors related to AIH recurrence. Fourteen of 475 patients received LT for AIH; 2 died perioperatively. Liver specimens (native and post-LT biopsies) from 12 other patients were reviewed and correlated with pre-and post-LT clinical course and outcome. Recurrent AIH was seen in 5 of 12 patients, 35 to 280 days post-LT as lobular hepatitis with acidophil bodies and lymphoplasmacytic infiltrate. Portal/interface hepatitis was seen with disease progression and 2 of 5 patients developed cirrhosis. Of 7 nonrecurrent patients, 1 had acquired hepatitis C with lobular/portal hepatitis and none developed cirrhosis. Histology suggestive of overlap syndrome was seen in 3 of 12 native livers with no effect on post-LT course or pathology. High-grade necroinflammation was present in native livers at LT in 5 of 5 cases with recurrent AIH and in 1 of 7 without recurrence (P < .01). Pre-LT disease duration, donor/recipient gender distribution, HLA studies, and rejection episodes did not correlate with AIH recurrence. We conclude that (1) recurrent AIH is not uncommon and was seen in 42% of patients with lymphoplasmacytic lobular, portal, and interface hepatitis; (2) acidophil bodies with lymphoplasmacytic cells are seen in early recurrent AIH; (3) recurrent AIH appears at variable time periods post-LT, and the progression is slow; and (4) high-grade inflammation in native liver at LT is a strong predictor of recurrent AIH. (HEPATOLOGY 2000;32:185-192.)

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